Circuit breaker trip device



Sept. 7, 1965 H. w. ARCHER ETAL 3,

CIRCUIT BREAKER TRIP DEVICE 3 Sheets-Sheet 1 Filed June 19, 1963INVENTORS HARRY W. ARCHER KE/TH W. KLEIN,

FIG. '2.

p 1965 H. w. ARCHER ETAL 3,205,325

CIRCUIT BREAKER TRIP DEVICE Filed June 19, 1963 3 Sheets-Sheet 2 F IG.4-

I I I l INVENTORS A rm Zn/Ey United States Patent Office 3,205,325Patented Sept. 7, 1965 3,205,325 CIRCUIT BREAKER TRIP DEVICE Harry W.Archer, New Britain, Keith W. Klein, Simsbury, and Kenneth J. Stokes,Wetherslield, Conn., as-

signors to General Electric Company, a corporation of New York FiledJune 19, 1963, Ser. No. 289,116 4 Claims. (Cl. 200-88) Our inventionrelates to electric circuit breakers of the type including separablecontacts and means for causing automatic opening of the contacts uponthe occurrence of predetermined electrical conditions, and moreparticularly, to the portions of such circuit breakers used to initiatesuch automatic opening, such portions being known as trip mechanisms ortrip units.

Automatic electric circuit breakers of the type used to controlsubstantial amounts of power, such for example as upwards of 100amperes, commonly include operating mechanism for manually operating thecontacts between open and closed circuit positions, the mechanismincluding. a member which is normally latched, but which is releasableto cause automatic opening or" the contacts. A trip mechanism or tripunit is also provided for causing release of the releasable member uponthe occurrence of predetermined current conditions. For convenience ofmanufacture and use, the trip mechanism or trip unit is oftenconstructed and assembled as a separate unit, so that a circuit breakerof a desired particular current rating may be provided by using a basiccircuit breaker assembly and mounting therein a particular selected tripunit, having the current rating desired. Such trip units commonlyinclude both thermal and magnetic operating tripping means. The thermaltrip means provides an inverse-time characteristic such that arelatively long time-delay is provided before tripping on the occurrenceof a relatively low current overload, and a relatively short time-delayis provided on the occurrence of a relatively high current overload. Themagnetic operating means, on the other hand, does not incorporate anytime-delay. It operates only at current overloads in the neighborhood ofthree to ten or more times the nominal current rating of the circuitbreaker. Since it comes into operation on the occurrence of such highoverload or short circuit conditions, its tripping action issubstantially instantaneous.

In accordance with a particular form of prior art electric circuitbreaker of the type described, the force required of the currentresponsive means to cause tripping is made to be substantiallyindependent of the contactclosing force exerted by the main operatingmechanism. This is accomplished by providing a secondary releasablemember carried by the trip unit itself, which, when released, strikes alatch member carried by the trip unit, which latch member then releasesthe main operating mechanism. There is no direct physical connectionbetween the secondary releasable member and the latch member whichreleases the main mechanism, and so there is no way in which forceexerted by the main operating mechanism can be reflected to thesecondary releasable member. A circuit breaker of the type referred tois shown in co-pending application Serial No. 192,192, filed May 3, 1962by L. P. Koval, now Patent No. 3,179,768, issued April 20, 1965, andassigned to the same assignee as the present invention.

While mechanisms of the type shown in the aforesaid Koval applicationoperate entirely satisfactorily in circuit breakers having short circuitinterrupting ratings up to about 10,000 amperes, they exhibit certaindisadvantages when used in circuit breakers applied on systems havingshort-circuit capacities above -20,000 amperes. This is because the useof a secondary releasable member, with its lost-motion travel,introduces a time-delay in the tripping sequence, even by the.magnetically operated trip means, of about to electrical degrees orabout .2 second. In other words, after the armature of the trippingmagnet has closed, about this much time is required before the primaryreleasable member is released. This delay does not cause any difficultyon circuits up to about 15,000 amperes short-circuit capacity. Abovethis level, however, the force of the current is sufiicient to blow thecircuit breaker contacts apart during the period of time betweenincidence of the short-circuit and the time when the main operatingmechanism has moved sufiiciently to cause opening movement of thecontacts. This permits arcing with consequent contamination of the arcextinguishing area, leading to eventual breakdown and failure.

In addition, it has been found that at such higher current levels,because of the time-delay mentioned, above, overheating of certainportions of the electrical circuit breaker occurs, particularly theheater portion which heats the current-responsive bimetal, often causingcomplete burn-out.

It is an object of the present invention to provide an automaticelectrical circuit breaker including a trip unit which maintains thethermal tripping means independent of the loading of the main operatingmechanism, and which nevertheless, does not introduce a time delay foroperation of the magnetic tripping means.

It is a further object of the invention to provide an electric circuitbreaker of the type described which is compact in size, and economicalto manufacture.

In accordance with the invention in one form, anelectrics circuitbreaker is provided of the type including at least one pair of separablecontacts and operating mechanism for manually operating the contactsbetween open and closed circuit positions, the operating mechanismincluding a primary releasable member and separable trip means forcausing release of the releasable member upon the occurrence ofpredetermined current conditions in the circuit. The separable tripmeans includes a primary latch member which normally engages andrestrains the primary releasable member. The trip unit also carries asecondary releasable member which is normally held against movement by asecondary latch member, disposed and arranged to be engaged by a thermalcurrent responsive element. The secondary releasable member haslostmotion travel between it and the primary latch member, so that noforce is reflected from the primary latch member to the secondaryreleasable member. In addition, magetic tripping means is providedincluding a magnet and an armature, and means directly connecting thearmature to the primary latch member, whereby movement of the magneticarmature is immediately accompanied by movement of the primary latchmember with no timedelay.

In addition, in accordance with another aspect of the invention, meansis provided for indicating following a tripping or automatic openingoperation, whether such automatic opening operation has occurred byreason of thermal tripping or by reason of magnetic tripping.

The invention will be more fully understood from the following detailed.description, and its scope will be pointed out in the appended claims.

In the drawings,

FIGURE 1 is a side elevation view, with part of the casing broken away,of an automatic electric circuit breaker incorporating the invention.

FIGURE 2 is a side elevation view, on enlarged scale, of a portion ofthe circuit breaker of FIGURE 1, showing the trip mechanism, portions ofthe trip unit casing being broken away;

FIGURE 3 is a view similar to FIGURE 2, but show- 3 ing only thethermally operated tripping means, in tripped condition;

FIGURE 4 is a view similar to FIGURE 3, showing only the magneticallyoperating trip means, in tripped condition;

FIGURE 5 is a top plan view of the tripping mechanism of FIGURES 1through 4, and

FIGURES 6 and 7 are fragmentary views of a portion of the indicatingmechanism of FIGURE 5.

In the drawings, the invention is shown as incorporated in an electriccircuit breaker comprising a generally rectangular insulating casingincluding a base 11 and a cover 11. Three pairs of relatively movablecontacts 12, 13 (only one pair shown), are provided in the base 10. Eachstationary contact 13 is connected to a corresponding line terminal 14by a line terminal strap 13A. Each movable contact 12 is carried by acontact arm 15. The movable contact arms 15 are adapted to be operatedin unison between open and closed circuit positions by means of anoperating mechanism, including a manually engageable handle member 16,projecting through an opening, not shown, in the casing cover 11. Theoperating mechanism includes a releasable member 17 and a pair of togglelinks 17A and 17B, interconnected by a knee pin 17C. The toggle isadapted to be operated by the handle 16 by means of an overcenter spring170. The operating mechanism shown is more fully described in Patent No.2,921,169, E. B. Judd et al., issued January 12, 1960, and assigned tothe same assignee as the present invention.

For the purpose of holding the member 17, and releasing it upon theoccurrence of predetermined current conditions through any of the threepairs of contacts 12, 13, tripping mechanism is provided comprising atrip unit designated generally at 18.

The trip unit 18 comprises a first insulating casing part 20 and asecond insulating casing part 21. The casing parts 20, 21 cooperated toform a closed box-like enclosure for the tripping mechanism.

A first set of three terminal members 22 is provided projecting throughopenings in the casing part 21. A second set of three terminal members25 is also provided projecting through openings in the casing part 20.Each pair of terminal members 22, 25, is connected to opposite ends ofan intermediate conductor 24. Each conductor 24 includes a generallyU-shaped intermediate portion 28 of smaller cross-section than said endportions, adapted to act as a heater.

The casing part 20 includes, adjacent each of the conductors 24, a pairof abutments or bosses, 29, positioned respectively at opposite sides ofeach conductor 24. A generally U-shaped magnet 30 is supported adjacenteach strap 24 in such a way that its bight portion rests against twocorresponding abutments 29. The side portions of each magnet 30 extendon opposite sides of one leg of the intermediate U-shaped portion 28 ofone of the conductors 24.

The leg of the intermediate U-shaped portion of the conductor 24 whichpasses through the magnet 30 is rigidly anchored to the casing part 20by means of a screw 31. Each screw 31 passes through an opening in thecasing part 20, through an enlarged clearance hole 32 in one leg of theintermediate portion 28 of the conductor 24, through a clearance hole inthe bight portion of the magnet 30, and into threaded engagement withthe other leg of the intermediate portion 28. Thus the screw 31 servesto press one leg of the portion 28 of the conductor 24 against the bightportion of the magnet 30 and this in turn against the abutments 29 ofthe casing part 20. The other leg of the portion 23, however, extendsfreely and with ample clearance through the space provided between themagnet 30 and the outer wall of the casing part 20.

Thermal tripping structure For the purpose of causing automatic openingin response to predetermined current overload conditions which arerelatively low in magnitude but of relatively long time duration, abimetallic strip 34 is provided at each pole of the circuit breaker,rigidly attached at one end thereof to the intermediate conductor 24adjacent one end of the U-shaped intermediate heater portion 28. Currentflow through the portion 28, therefore, causes heating in theintermediate portion 28 because of its restricted cross-section. Thisheat is transmitted by conduction to the bimetallic strip 34, causingdeflection thereof. Each of the bimetallic strips 34 carries anadjusting or calibrating screw 35 adjacent its free end which, when thebimetallic strip deflects, engages a thermal trip bar 36 and causes itto rotate in a clockwise direction, as viewed, about the pivot pins 37.

The parts of the mechanism which operate when thermal tripping occursare shown particularly in FIGURE 3, the parts being shown in thecondition which they occupy immediately after tripping has occurred.

The trip bar 36 carries an ambient compensating bimetallic strip 52rigidly attached thereto at one end, the strip 52 having its other enddisposed and arranged to engage a secondary latch member 38, see FIGURES2 and 3. The secondary latch 38 serves to restrain a secondaryreleasable member 39 from movement. The secondary latch member 38 isalways biased toward latching position by means of spring 38A, and thesecondary releasable member 39 is contantly biased for rotation incounterclockwise direction by means of the spring 40.

When the secondary releasable member 39 is released by the latch member38, it therefore rotates in counterclockwise direction, causing theprojecting portion 41 thereof to engage a portion 42 of the primarylatch member 43 which is pivotally supported on a pin 44. This releasesthe primary latch member 17 and permits automatic opening of thecontacts.

It will be observed that since the trip bar 36 extends across all threepoles of the circuit breaker and can be engaged by the calibrating screw35 of each of the bimetallic strips 34 in each of the poles, thermaltripping as described will occur upon sufiicient deflection of thebimetallic strip 34 in any one of the poles.

Following release of the secondary releasable member 39 by the latchmember 38, some time is required for it to rotate far enough to engagethe portion 42 of the primary latch member 43 and to move this farenough to initiate tripping.

Magnetic tripping structure In accordance with the invention, magnetictripping means is also provided, comprising the three magnets 30 withenergizing conductors 28, previously described, and also three pivotallysupported magnetic armatures 45 pivotally supported on the pivot pins37. Also supported on the pivot pin 37 is a generally channel-shapedmember 47, which has connected thereto an elongated sliding link or hook48 having a hook-like projection 49 at the other end thereof. The member48 is guided for sliding movement on a pin 50 which extends through aslot 48A. The member 47 also carries a side-wise extending magnetic tripbar 51 having portions extending across all three poles of the circuitbreaker. Upon the occurrence of high short-circuit currents, one or moreof the armatures 45 is attracted to its magnet 30, causing the extension45A of the armature 45 to engage the magnetic trip bar 51, causingrotation of the member 47 and moving the link 48 to the left as viewedin FIGURE 2. This causes the hook portion 49 of the link 48 to engagethe bent-over portion 42 of the primary latch 43, thereby releasing theprimary releasable member 17.

It will be noted that this tripping action by the magnetic trippingmeans takes place without movement of the secondary latch member 38 orthe secondary releasable member 39.

Each of the armatures 45 is biased toward non-operated position by meansof a return spring 45A which is adjustably positioned by an adjustinglever 61 carried by an adjusting screw 61A which is pivotally supportedon an abutment 62 of the circuit breaker casing.

The parts which operate when magnetic tripping occurs are shownparticularly in FIGURE 4, the parts here also being shown in theposition which they occupy at the instant when tripping occurs.

In accordance with the invention, the two systems, one thermal and theother magnetic, for causing release of the primary latch member 43,operate independently of each other. Thus instantaneous release of theprimary latch member 17 is provided, even though the thermal trippingmeans is isolated from the primary latch member and even though a shorttime delay is involved when such thermal tripping occurs.

In accordance with another aspect of our invention, means is providedfor indicating the occurrence of magnetic tripping as distinguished fromthermal tripping. For this purpose, an indicator 39A is provided on thesecondary releasable member 39, and a bracket 55 is provided on the tripunit casing part 21, hearing the markings magnetic and thermal. Theindicator 39A is normally positioned adjacent the word magnetic, andonly when the member 39 is released by the secondary latch member, doesit move to the thermal position. When magnetic tripping occurs,therefore, the indicator 39A does not move, but remains adjacent theWord magnetic." When the user observes that tripping has occurred, suchtripping being indicated, for example, by the movement of the operatinghandle 16 to trip indicating position as is well known in the prior art,he needs only to look at the indicator 39A to observe that such trippingoccurred because of a sudden high overload rather than a sustained slowoverload.

Likewise, if tripping occurs by reason of a slow, sustained overload,the member 39 will be released to cause tripping, thereby moving theindicator 39A to the thermal indicating position.

The trip indicating pointer 39A may be observed by removing the casingcover 11, or if desired, by providing an opening, not shown, in thecasing cover, through which the indicator may be observed.

In a series of tests on a circuit capable of delivering 50,000 amperesat 240 volts, the average interrupting time in terms of electricaldegrees of a particular prior art circuit breaker was 204 degrees fromthe incidence of the short circuit. With the same circuit breaker,modified to incorporate the present invention, the interrupting time onthe same test was 131 electrical degrees. The time required forinterruption of the short circuit in the above tests was thereforereduced 73 electrical degrees out of a total of 204 electrical degrees,or a reduction of about 36%. When dealing with short circuit currents ofthis magnitude, a reduction of this nature, of over /3 of the arcingtime, significantly prolongs the life of the circuit breaker andsignificantly reduces the likelihood of failure of the breaker tointerrupt.

While the invention has been disclosed in only one particularembodiment, it will be readily apparent that many modifications mayreadily be made, and I therefore intend by the appended claims, to coverall such modifications as fall within the true spirit and scope of theinvention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An electric circuit breaker comprising:

(a) a generally rectangular insulating main casing;

(b) at least two separable contacts;

(c) operating mechanism for moving said separable contacts between openand closed circuit positions;

(d) said operating mechanism including a primary releasable membermovable when released to cause automatic opening of said contacts;

(e) a primary latch normally engaging and restraining said primaryreleasable member;

(f) a removable trip unit mounted in said main casing;

(g) a secondary releasable member carried by said trip unit and movablewhen released to cause releasing movement of said primary latch member;

(h) said trip unit including a secondary latch member normally engagingand restraining said secondary releasable member;

(i) said trip unit including a thermal current responsive meansresponsibe to current passing through said separable contacts forcausing release of said secondary latch member;

(j) at least one electromagnet carried by said trip unit;

(k) said trip unit including means for energizing said electromagnet inresponse to current flowing through said separable contacts;

(I) said trip unit including a magnetic armature disposed and arrangedto be attracted to said electromagnet upon the occurence ofpredetermined energization of said electromagnet;

(m) a releasing member pivotally connected to said armature;

(11) means slidably guiding said releasing member for reciprocatingmovement in response to pivotal movement of said armature;

(0) said releasing member having a hook portion disposed and arranged toengage said primary latch member to positively move said primary latchmember to releasing position when said armature moves to attractedposition.

2. An electric circuit breaker comprising:

(a) a generally rectangular insulating main casing;

(b) at least two separable contacts;

(0) operating mechanism for moving said contacts between open and closedcircuit positions;

(d) said operating mechanism including a primary releasable membermovable when released to cause automatic opening of said contacts;

(e) a primary latch member normally engaging and restraining saidprimary releasable member;

(f) a removable trip unit comprising an insulating casing mounted insaid main casing;

(g) at least one electromagnet mounted in said trip unit casing;

(h) means for energizing said eelctromagnet in response to currentflowing through said separable contacts;

(i) a magnetic armature disposed and arranged to be attracted to saidelectromagnet upon the occurrence of predetermined current energizationof said electromagnet;

(j) a releasing member slidably mounted on said trip unit casing andincluding a hook portion disposed and arranged to engage said primarylatch member;

(k) connecting means connecting said armature memher to said releasingmember whereby movement of said armature to attracted positionpositively moves said primary latch member to releasing position.

3. An electric circuit breaker comprising:

(a) a generally rectangular insulating casing;

(b) at least three pairs of separable contacts mounted in saidinsulating casing;

(c) operating mechanism mounted in said insulating casing for movingsaid separable contacts in unison between open and closed circuitpositions;

(d) said operating mechanism including a primary releasable membermovable when released to cause automatic opening of all of saidcontacts;

(e) a primary latch member normally engaging and restraining saidprimary releasable member;

(f) a removable trip unit comprising a generally rectangular insulatingcasing, receivable in said main circuit breaker casing;

(g) at least three electromagnets in said trip unit casing, each of saidelectromagnets corresponding to one of said pairs of separable contacts;

(11) means for energizing each of said electromagnets in response tocurrent flowing through said corresponding pair of separable contacts;

(i) a magnetic armature for each of said electromagnets disposed andarranged to be attracted to said corresponding electromagnet upon theoccurrence of predetermined energization of said electromagnets;

(j) a member pivotally supported in said trip unit cas- (k) a trip barcarried by said pivotally supported member and having portions extendingadjacent each of said magnetic armatures, whereby movement of any ofsaid armatures towards its corresponding electromagnet causes movementof said pivotally supported member;

(1) means directly connecting said pivotally supported member to saidprimary latch member, whereby movement of any of said magnetic armaturesto attracted position with respect to its corresponding electromagnetspositively causes releasing movement of said primary releasable member.

4. An electric circuit breaker as set forth in claim 3 said circuitbreaker also comprising:

(in) thermal current responsive means carried by said trip unitcorresponding to each of said pairs of separable contacts;

(n) a secondary releasable member carried by said trip unit casing;

(o) a secondary latch member carried by said trip unit casing andnormally engaging and restraining said secondary releasable member;

(p) said thermal current responsive means being disposed and arranged toengage said secondary latch member to cause releasing movement of saidsecondary latch member upon the occurrence of predetermined currentconditions through any one of said pairs of separable contacts, and

(q) said thermal current responsive means and said magnetic currentresponsive means acting independently of each other on said primarylatch member to cause releasing of said primary latch member.

References Cited by the Examiner UNITED STATES PATENTS 2,419,125 4/47Dorfman et a1. 2,821,596 1/58 Bires et a1. 2OO88 2,981,811 4/61 Stevenet al. 20088 BERNARD A. GILHEANY, Primary Examiner.

2. AN ELECTRIC CIRCUIT BREAKER COMPRISING: (A) A GNERALLY RECTANGULARINSULATING MAIN CASING; (B) AT LEAST TWO SEPARABLE CONTACTS; (C)OPERATING MECHANISM FOR MOVING SAID CONTACTS BETWEEN OPEN AND CLOSEDCIRCUIT POSITIONS; (D) SAID OPERATING MECHANISM INCLUDING A PRIMARYRELEASABLE MEMBER MOVABLE WHEN RELEASXED TO CAUSE AUTOMATIC OPENING OFSAID CONTACTS; (E) A PRIMARY LATCH MEMBER NORMALLY ENGAGING ANDRESTRAINING SAID PRIMARY RELEASABLE MEMBER; (F) A REMOVABLE TRIP UNITCOMPRISING AN INSULATING CASING MOUNTED IN SAID MAIN CASING; (G) ATLEAST ONE ELECTROMAGNET MOUNTED IN SAID TRIP UNIT CASING; (H) MEANS FORENERGIZING SAID ELECTROMAGNET IN RESPONSE TO CURRENT FLOWING THROUGHSAID SEPARABLE CONTACTS; (I) A MAGNETIC ARMATURE DISPOSED AND ARRANGEDTO BE ATTRACTED TO SAID ELECTROMAGNETIC UPON THE OCCURRENCE OFPREDETERMINED CURRENT ENERGIZATION OF SAID ELECTROMAGNET; (J) ARELEASING MEMBER SLIDABLY MOUNTED ON SAID TRIP UNIT CASING AND INCLUDINGA HOOK PORTION DISPOSED AND ARRANGED TO ENGAGE SAID PRIMARY LATCHMEMBER; (K) CONNECTING MEANS COPNNECTING SAID ARMATURE MEMBER TO SAIDRELEASING MEMBER WHEREBY MOVEMENT OF SAID ARMATURE TO ATTRACTED POSITIONPOSITIVELY MOVES SAID PRIMARY LATCH MEMBER TO RELEASING POSITION.